A magnetic material is composed of a number of domains. Each domain contains parallel atomic moments and is magnetized to saturation, but the directions of magnetization of different domains are not necessarily parallel. Local preferred directions of magnetization depend upon the underlying microscopic structure of the material. Magnetic recording media microstructure generally includes grains or particles comprising regions of constant crystal structure or geometry. The local directions of easiest magnetization depend upon the geometry of the crystals. In the absence of an applied magnetic field, adjacent domains may be oriented in different directions, controlled by the underlying grain structure. The resultant effect of all these various directions of magnetization may be zero, as is the case with an unmagnetized specimen. When a magnetic field is applied, domains nearly parallel to the direction of the applied field become more prevalent at the expense of the others. A further increase in magnetic field causes more domains to rotate and align parallel to the applied field. When the material reaches the point of saturation magnetization, all domains are parallel to the applied field and no further domain growth or rotation would take place on increasing the strength of the magnetic field.
The ease of magnetization or demagnetization of a magnetic material depends on material parameters including composition, crystal structure, grain orientation, and the state of strain. The magnetization is most easily obtained along the easy axis of magnetization but most difficult along the hard axis of magnetization. A magnetic material is said to possess a magnetic anisotropy when easy and hard axes exist. On the other hand, a magnetic material is said to be isotropic when there are no easy or hard axes.
In a perpendicular recording media, magnetization is formed easily in a direction perpendicular to the surface of a magnetic medium, typically a magnetic recording layer on a suitable substrate, resulting from perpendicular anisotropy in the magnetic recording layer. On the other hand, in a longitudinal recording media, magnetization is formed in a direction in a plane parallel to the surface of the magnetic recording layer, resulting from longitudinal anisotropy in the magnetic recording layer.
Thin-film magnetic recording media require small exchange decoupled magnetic particles. Decoupling is commonly achieved by having a non-ferromagnetic material between the ferromagnetic particles. This non magnetic region has been formed in the prior art by films having a higher percent composition of either chromium, boron, or an oxide material at the boundaries between magnetic particles than within the magnetic particles. Separation of magnetic particles is imperfect, and some separation mechanisms are difficult to apply in a manufacturing process. An improved magnetic grain isolation method is desired.
The current perpendicular recording media (so called granular media) is processed using O2 reactive sputtering technique, and oxide dispersants to achieve smaller and physically isolated grains, and also uses a thick amorphous soft magnetic under layer (SUL) such as Fe, Ni, or Co-based alloy films as a mirror pole for recording performance. The Fe-based SUL forms a part of the media design. Since the SUL is based on iron, these alloy films are prone to severe corrosion. Because these Fe-based SUL films and other media layers are hard to cover at disk edges (chamfer area) as well as at mechanical defects (voids, pits etc) by the carbon overcoat material, harsh environmental conditions (HCl and water vapors at ambient and elevated temperatures) make the edges and other mechanical defects at the data zone area severely susceptible to corrosion. This produces edge corrosion at the edges and defect corrosion at voids and other mechanical defects. Hence, solution(s) that provide a corrosion-resistant SUL in the perpendicular media design and prevents the edge as well as the mechanical defect corrosion of the perpendicular media is desired.